The present invention relates to sprocket assemblies for a bicycle, and more particularly to a sprocket assembly including a sprocket carrier, first and second sprockets mounted one on each side of the sprocket carrier and a third sprocket arranged between the first and second sprockets.
A sprocket assembly for a bicycle includes several sprockets with decreasing diameters that are supported concentrically by one or more sprocket carriers. The desire to increase the number of sprockets included in the assembly and the desire to provide a lightweight construction have placed stringent demands on the configuration of the sprocket assembly. Also, the close gear ratio configuration of the sprockets and the small differences between the diameters of adjacent sprockets place stringent demands on the sprocket assembly configuration.
The European patent EP 0 712 780 A1 discloses a sprocket assembly that includes a stepped carrier having three support arms for receiving a plurality of sprockets. The stepped carrier is supported on the largest and smallest sprockets and receives a sprocket on each step of the carrier. The largest and smallest sprockets and the carrier are joined nonrotatably to the hub and torque is transmitted through the largest and smallest sprockets to the hub from the other sprockets. The sprockets between the largest and smallest sprockets are retained on the arms of the carrier by delimiting lugs.
The European Patent EP 0 510 371 B1 discloses a sprocket carrier for mounting a plurality of sprockets. The carrier includes radially extending stepped support arms that receive the individual sprockets. Screws attach the sprockets to the support arms. To reduce weight, a back of each support arm is cut out.
The European Patent EP 0 849 155 A2 discloses a sprocket assembly having fourteen sprockets and three subassemblies. The first subassembly includes a carrier having radially extending arms that include axially offset steps for rivet attachment of the sprockets. The second subassembly includes a carrier having spokes for rivet attachment of one sprocket to each side of the carrier. The third subassembly includes individual sprockets directly connected to the hub and separated by spacers.
The European Patent EP 0 765 802 B1 discloses a sprocket assembly that includes two subassemblies wherein the first subassembly includes a carrier having radially extending arms for receiving sprockets and the second subassembly includes individual sprockets attached directly to the hub which are separated by spacers. Sprockets with small differences in tooth count are attached to both sides of the carrier by the same rivets.
The sprocket assemblies disclosed in the above patents illustrate the development from, the original, individually fitted-together sprocket assemblies to the complex sprocket assemblies having several subassemblies of sprocket carriers for receiving the individual sprockets. Potentials for improvement still exists in terms of design complexity, number of functional parts, and overall size, as well as torsional stiffness and cost reduction.